Windex does a lousy job in cleaning my windows (leaves a film). I would never use it on one of my lenses. I use ROR (Residual Oil Remover) a product made for lens cleaning, and it, along with a microfiber cloth does a great job of lens cleaning.
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WSSA #318

Your are right, Windex is awful for cleaning windows and the pros never use it. The most respected name in professional window cleaning is Ettore and their window cleaning solution does
not
contain ammonia. That said, I would not use it either to clean my lenses! I use Peca's Formula MC (made in USA!).
Here is some good advice on lens care.
http://www.earthboundlight.com/phototips/lens-cleaning.html

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Best regards,
Jon

Yet one of the most repsected optical designers for astronomical telescopes/eyepieces actually recommends windex:

Like many things in life, it's how you use something, not the thing itself, that determines whether it's good or bad. Windex, when used properly, is an excellent tool for helping to clean optical equipment. Use poor technique, and it won't end up well.

The primary reason, btw, that Windex leaves streaks is because the window is dirty and the windex merely moved the dirt around (you need to remove the windex & the dirt it contains). If windex absorbs the dirt, but you simply let the windex dry, where does the dirt go? Right back onto the glass. No substance, whether it be windex or another cleaner, can make dirt disappear. All it does is help move it into something that you can more easily remove it with (in this case, dissolving the dirt). This lack of understanding (or lack of technique to wipe up the windex) is the major cause, of windex-based streaks, IMO. If you remove the windex properly after using it to loosen and collect the dirt/gunk, it will take the dirt with it.